This invention relates to a method and apparatus for the production of nitrogen fertilizers and more particularly to a portable, home-use unit which, for example, may be attached to a garden hose for production of dilute nitric-nitrous acid fertilizer or, by the addition of lime, calcium nitrate fertilizer.
Nitrogen is an essential material in the production of fertilizers. While it is the major component of the atmosphere (79 percent in dry air), nitrogen can be incorporated into most living systems only in the "fixed" form and nitrogen is less abundant in its fixed form. For gardening and yard maintenance it is desirable to supplement the natural sources of fixed nitrogen with chemical fertilizers. Typically, chemical fertilizers contain nitrogen which is fixed by industrial methods in which nitrogen is combined with hydrogen to form ammonia.
The principle industrial method for producing ammonia is the Haber process. In the Haber process, one molecule of nitrogen and three molecules of hydrogen combine at elevated temperature and pressure in the presence of a catalyst to form two molecules of ammonia. The hydrogen utilized in the Haber process is obtained primarily from natural gas and liquid hydrocarbons. As long as there is a ready and inexpensive supply of hydrogen, the Haber process is unequaled in cost and efficiency for producing fixed nitrogen fertilizers.
However, because of the energy crisis the source of supply of hydrogen has decreased, and there has been a concomittant rise in the price. The demand for fixed nitrogen continues to grow, however, due to world population increases and the introduction of nitrogeneous fertilizers in the underdeveloped regions of the world. Thus it would appear likely that the cost of fixed nitrogen will continue to increase.
Accordingly, an investigation has begun into nitrogen fertilizer production methods other than the Haber process. See, for example, Safrany, "Nitrogen Fixation", Scientific America, Vol. 231, No. 4, pp. 64-80 (1974), wherein the following possible alternatives are discussed: biological fixation, metallo-organic, thermal activation, and low temperature ionization.
Principally, these alternatives strive to produce various nitrogen oxides, which with water addition will form nitric acid (HNO.sub.3). That is depending on conditions, the reaction of nitrogen gas and oxygen gas will form one or more of the following nitrogen oxides: NO, N.sub.2 O.sub.3, NO.sub.2 or N.sub.2 O.sub.4. Safrany states that it is easiest to discuss the reaction as producing nitric oxide (N.sub.2 + O.sub.2 .fwdarw. 2NO). But it should be realized that nitric oxide (NO) readily combines with oxygen at room temperature in an exothermic reaction to form nitrogen dioxide (NO.sub.2). Thus, the reaction N.sub.2 + 2O.sub.2 .fwdarw. 2NO.sub.2 can be said to be favored since nitrogen dioxide has the lowest heat of formation.
In any event, for production of the nitrogen oxides, Safrany finds low-temperature ionization to be the most attractive alternative. He states:
"Low-temperature ionization has the significant advantage that in principle all the molecules of the gas can be ionized or excited. The activation can be accomplished by subjecting the air to an electrcal potential of a few thousand volts, so that a low-temperature discharge is initiated, or by exposing air to an intense flux of ionizing radiation inside a nuclear reactor. In either case the gas molecules are bombarded by fast-moving ions and the collisions are inelastic. The resulting cascade of reactions can produce a substantial yield of nitrogen oxides. PA1 As in all endoergic processes, the telling factor in calculating the feasibility of low-temperature activation is the cost of energy. If the source of energy is electricity, its cost would seem to forbid fixation by air activation as a commercial enterprise. The "chemonuclear" technique, on the other hand, utilizes a remarkably cheap form of energy: the kinetic energy of the nuclear fragments produced by the fission of a uranium nucleus." PA1 "The percentage of nitric oxide in the equilibrium N.sub.2 + O.sub.2 .revreaction. 2NO is: PA1 In order to obtain a fair yield an exceptionally high temperature must be employed; 4200.degree. T. corresponds approximately to aht attained in the electric arc, and a favourable yield can then be obtained. At this temperature, however, not only the establishment of the equilibrium, but also the back decomposition, is very rapid, and it is necessary to bring the nitric oxide formed to a region of lower temperature as quickly as possible to avoid a great part of it being lost. This is carried out by having the arc suitably constructed, so that either it is spread out by an electro-magnet into a thin disc of flame, through which the N--O mixture (air) is blown, or the arc is kept in motion in the form of a sinuous, narrow, spiral band, or is forced into a water-cooled iron tube. In this way, on a laboratory scale, up to 8 percent of the mixture has been converted to a nitric oxide, and in technical operations, up to 2.5 percent. It is not only the thermal effect of the arc which is responsible for the formation of nitric oxide; under the influence of strong electric fields (silent discharges), oxygen and nitrogen are decomposed into atoms which can then combine to form nitric oxide. This process must also play a part in the arc process."
As can be seen, even within the broad category of low-temperature ionization, Safrany prefers the chemonuclear approach because of the economics involved. The rejected alternative is use of an electrical arc discharge process.
The basics of using an electrical arc discharge for production of nitrogen oxides are well known. See, for example, Ephram, Inorganic Chemistry, Fifth Edition-Revised, 1949, pp. 680-704. However, the art has also long recognized that difficulties exist with the arc discharge process. Thus in Ephram at page 683 it is stated:
__________________________________________________________________________ Temperature 1500.degree. 2000.degree. 2500.degree. 2900.degree. 3200.degree. 4200.degree. T. Per cent 0.1 0.61 1.79 3.20 4.43 10 __________________________________________________________________________
As can be seen from the above, while a process of low temperature ionization for the production of fixed nitrogen is known, the economic feasibility of electric arc activation of air as a means of fixation has been considered doubtful. The total cost per pound of using electrical low temperature ionization for nitrogen fixation is indicated by the Safrany article to be 15 times the cost of chemonuclear low temperature ionization and 21/2 times the cost of the Haber process.
Such methods of production are of course not feasible for a home-use unit which fixes nitrogen and injects it into the water line supplying moisture to the yard or garden. Production of nitrogen fertilizer by a unit which automatically adds the fertilizer to the water flowing through a garden hose would eliminate the distribution and transportation costs which are responsible for a large portion of the delivery cost of industrially produced nitrate fertilizer. Additionally, if the arc discharge process were used, nitrogen oxides would be formed from air and the home owner would not need to keep a supply of fertilizer on hand. Also, fertilization of the yard or garden could be accomplished without the time consuming spreading required when dry fertilizers are used.
Thus a need exists for a practical, efficient, economical source of nitrogen fertilizer for home use, particularly one capable of producing nitrogen oxides and injecting them into a water line supplying moisture to the yard or garden of a home.